Electric discharge tube with locating member



Oct. 31, 1950 w. A. ROOVERS ET AL 2,528,246

ELECTRIC DISCHARGE TUBE WITH LOCATING MEMBER Filed Dec. 6, 1947VV.A.ROOVERS, E PRAKKE O.L.VAN STEENIS & I J.M.DE JONG NVE NTOR 5 BYAGENT Patented Get. 31,

ELECTRIC DISCHARGE" TUeE WITH LOCATING MEMBER Wilhelmus AntoniusRoovers, FritsPr'akk'e'," Otto Louis van Steenis, and Isidorus JohannesMaria de Jong, Eindhoven, Netherlands; assignorst'o Hartford NationalBank and Trust'Company; Hartford, Conn., as trustee Application December6, 1947, Serial No. 790,103 In the Netherlands October 11, 1946 Section1, Public Law 690, August 8, 1946 Patent expires October 11, 1966 1Claim. 1

This invention relates to electric discharge tubes and more particularlyto tubes comprising a locating member.

In order to ensure correct insertion of a tube into its holder, it isknown to position the contacts of the tube at unequal distances from oneanother. Correct insertion of such a tube into a holder is difficult,however, if the holder is not readily accessible and the arrangement ofthe tube contacts cannot be compared with that of the contacts in theholder. Consequently, one frequently resorted to providing a mark on theside-wall of the cap or bulb and on the top of the holder in addition tosuch unequal arrangement of'the tube contacts. Furthermore, with regularor irregular positioning of the tube contacts it is known to utilize aso-called locating member, for example in the form of a central bush,which may serve as a screening bush for the exhaust tube and also as acentering bush.

Finally, it has been suggested to use a locating member provided on theexternal periphery of the tube, in which event the lower extremity ofthe tube itself serves for centering. The locating member is then formedin the shape of a thickened portion of the wall of a moulded tube bottomor of a moulded bulb. In order to avoid great strain in this thickenedportion of the glass wall and hence the risk of cracking, said locatingmember is required to be provided at preferably at least 5 mm. from theplace of sealing. However, such a construction is not suitable for tubeshaving a plane base disc secured to a thin-walled, blown glass bulb.Providing the locating memvide a locating member on an electricdischarge tube which is made by a simple method and is resistant tobreakage during the handling of the tube.

Other objects and advantages will become apparent from the followingspecification.

According to the invention, an electric discharge tube having athin-walled blown glass bulb is provided with a protuberance in the bulbwall, the thickness of the protuberance being smaller or at the utmostequal to the thickness of the bulb wall. The protuberance is filled upwith glaze or similar material that adheres well to the glass. shouldexhibit approximately the same coefiicient of expansion as the glass andshould be of low melting point so that, upon heating, it will meltbefore the glass of the protuberance softens.

An electric discharge tube provided with the locating member accordingto the invention has the following advantages. The wall thickness of thebulb is substantially even so that the disr tance between the locatingmember and the place of scaling is not of critical importance. Further.-more, such a protuberance may be formed in verysimple manner, forinstance by local heat-f ing of' the bulb after being shaped and bypush, ing the glass of the bulb outwardly by means of a small metal rodconsisting of a metal having a high melting point, such as tungsten.With respect to the method in which the protuberance is formed duringthe blowing process of the bulb, the afore-mentioned method has thefurther ad vantage that the glass rapidly cools down on being touched bythe tungsten rod and hence will be less soft than the surrounding glass,thus pre-l venting the wall-thickness at the top of the pro-. tuberancefrom becoming too small. This is of great importance since it is justthe top of the protuberance which has to be resistant to the heaviestshocks.

Due to the filling of the protuberance with glaze or similar material,the thin-Walled mem: ber withstands even rough handling which other-rwise might cause breakage. Since the filler is not integral with theglass wall, as is the case with the glass of a locating member formed bya locally thicker portion of the glass wall, the disadvantages of such asolid locating member, that is the danger of cracking due to internalstrain, do not occur in this case, while the advantages of such a solidmember are still present.

It is evident that such a protuberance cannot in practice be formed inthe case of a moulded bulb since local strong heating of such a bulb,which naturally is required to have a much greater wall thickness than ablown bulb, is attended with a very great risk of cracking. Such aprotuberance cannot in practice be formed during the moulding process sothat it was necessary in this case to utilize a solid locating memher.

It is known per se to provide the top of a blown bulb with a circularprotuberance. This pro- Preferably, the glaze or the like.

tuberance does not serve as a locating member. Such a protuberance ofcomparatively large size may, however, readily be formed during blowing.Furthermore, it is known to keep a tube in position in a holder by meansof springs which engage in one or more re-entrant parts provided in thewall of the bulb. However, such a re,- entrant part cannot serve as alocating member and does not cause such difficulty on being formed sincea re-entrant part may readily be formed already during blowing, as itstop runs little risk of being damaged.

In order that the invention may be more a clearly understood and readilycarried into eifect, it will now be described more fully by reference tothe accompanying drawing.

Fig. 1 is a sectional view of a locating member according to theinvention, and

Fig. 2 is a plan view of such a locating member.

In the figures, reference numeral I indicates the thin-walled blownglass bulb which is closed by means of a base 2. Pins 3 are sealed intothe base 2. The bulb exhibits a locating member 4, which is constitutedby a protuberance having a wall thickness substantially equal to that ofthe bulb, the protuberance being filled up with glaze 5. Such afilled-up locating member is of substantially the same rigidity as alocating member of solid glass without exhibiting the disadvantages ofthe latter.

Upon inserting the tube into its holder the lower extremity of the bulbserves to center the tube, and turning the tube until the member 4engages in a recess of the upper edge of the holder ensures correctpositioning of the contacts with respect to the contacts of the holderso that the tube may subsequently be pushed down in the holder. Toprevent the tube from falling out of its holder, a spring may embracethe locating member 4 in known manner.

Since no metal parts are required for the centering and locatingoperations, such a tube is highly adapted for use on high frequencies.Furthermore, the tubes may be of very small size without the positioningof the locating member causing diificulty.

What we claim is:

' An electric discharge tube comprising a thin walled cylindrical blownglass bulb having a longitudinal axis, a protuberant locating memberportion of said bulb radially offset from said longitudinal axis of saidbulb, said portion having a wall thickness substantially equal to thatof the said bulb, and a filling material in said protube-rant portionreinforcing said protuberant portion, said material consisting of aglaze of a melting point lower than and a temperature coefiicient ofexpansion substantially equal to that of the glass of said protuberantportion.

WEI-TELMUS ANTONIUS ROOVERS. FRITS PRAKKE.

OTTO LOUIS VAN STEENIS.

ISIDORUS J OHANNES MARIA DE J ONG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

